Redispersing and compounding rubber



Patented Oct. 30, 1951 REDISPERSING AND COMPOUNDING RUBBER Arthur Pollak, New York, and John J. Keilen, Jr., Forest Hills, N. Y., assignors to West Virginia Pulp and Paper Company, New York, N. Y., a

corporation of Delaware No Drawing. Application February 26, 1948, Serial No. 11,313

28 Claims.

Our invention relates to improvements in rubber compounding.

In the usual method of rubber compounding the rubber is first coagulated from its state of suspension in the original latex. The crude rubber, whether natural or artificial, is then masticated in a suitable type of mill, following which plasticizers and softeners are added. Then at the appropriate time the fillers, other chemicals, such as accelerators, anti-oxidants and vulcanizing agents are added, the milling being continued to disperse the compounding ingredients in the rubber. Alternatively it has been proposed to add a suspension of reinforcing agent or pigment, as for example carbon black, to the latex and to precipitate the rubber and pigment together, after which the other ingredients are added by milling. Because the milling operation requires considerable hand labor and power, much effort has been expended in the attempt to devise some other method of incorporating compounding agents in rubber. Thus many attempts have been made to utilize the product obtained by spray drying ordinary rubber latex either as such or with added chemicals. Such processes while offering promise have fallen short of complete success mainly for the reason that it has heretofore not been practicable to separate from the rubber the other solids naturally occurring in the latex. In natural latex such other solids consist largely of protein material whereas in the case of artificial rubbers a considerable quantity of soap is present.

In accordance with our invention rubber from either natural or artificial latices may be precipitated, the precipitates collected and washed free of impurities without causing the rubber particles to coalesce. In this state the rubber particles of the precipitate or filter cake may be reconverted to the original dispersion minus the impurities. Such dispersion may be mixed with the appropriate compounding agents and the entire mixture dried and the dried product molded and vulcanized with little or no milling operation.

- Our invention is predicated upon our discovery that rubber can be coprecipitated with an agent which surrounds the rubber particles and keeps them separated from each other so that they can be easily redispersed. The best substance we have found to date having this property is lignin.

A coprecipitate of lignin and rubber containing '7 lbs. of lignin per 100 lbs. of GR-S (butadiene, styrene copolymer) was obtained in the following manner:

A solution of lignin was first made by preparing a slurry of 25 lbs. thereof in lbs. of water and then adding 10 lbs. of 50% caustic soda. The resulting lbs. of solution contained 25% lignin in the form of sodium lignate.

20 lbs. of GR-S latex containing anti-oxidants and short stop agents having a rubber content of 5 lbs. was then mixed with 10 lbs. of the 25% lignin solution. An 0.8% sulfuric acid solution was prepared by adding 1.8 lbs. of 60 B. (77.7%) sulfuric acid to 178 lbs. of water. This solution was heated to 194 F. and the lignin-latex mixture slowly added thereto while agitating thoroughly. The mixture was then filtered and washed. After washing, the coprecipitate was removed from the filter and placed in a mixer of the bowl and whip type. The usual compounding chemicals were then added as dry powders except for the plasticizer BRT (coal tar oil product) which is a tarry fiuid. This was added as a liquid. A total mixing time of45 minutes was used to insure adequate dispersion of the chemicals and admixture with the dispersed rubber particles. The mixture of coprecipitate and chemicals was put into shallow pans and dried for 48 hours at 70 C. Following are the proportions of chemicals used, parts by Weight:

Lignin GR-S-50 Sulfur 2.5

' The dried mixture was sheeted out on the roll mixer which required 5 minutes time. It was then cured and tested with results as follows:

4 and under conditions such that the temperature of the mixture will preferably not exceed 350 F.

A sample prepared as per the foregoing exam- At ple involving the redispersion of GR-S, carbon Property 2? 292 F. black and lignin in the proportions respectively 60 of 100:45z5 together with compounding ingredients tested as follows: 300% modulus, p. s.i 900 1,010 910 Tensile Strength, p. s. i l, 850 2,080 2, 010 $2 35 2333 per cent 2g 552 52 Cure Min. 2 {i Tcarresistance,lbs./in::::IIIIII: 250 240 240 Property 30 45 The time f mixing was greater than necest i'fiiitt trffiiiiijjjijjiijjjijjii 2,323 2, 338 it??? sary and could be reduced considerably. Howa g g i g? 3% ever, even without this reduction th p w r l5 ret st-reti e,itii iiiiijiijiiijiji:1:: 186 206 172 ing is very considerable. A half horse power p p was usgd on the mlxer wheteas the im The action above called for of milling the dried mlxmg operatlonperformed on f coprempl' mixture of redispersed rubber and compounding tates would require at least 45 mmutgs usmg materials to form a sheet, preliminary to curing, about 5 horse power In another expenment results in most instances in an increase in slight quantity of water was used to redisperse strength. 7 the filter Q Lignin is generally identified as that com- The redlspersed copreclpltates mlxed Wlth ponent of wood which is insoluble in 72% H2804 ing chemicals may if desired be sprayed on any it a compound of carbon hs'ldrogen and suitable surface as a coating or such mixture may 5 gen and sometimes of the foregoing plus sulfur be applied to a textile, paper or other surface with is further characterized by being Somme either a knife or roll coating device similar to solvents such as dioxane and by havingxsl'lfficient those used for applying pigments to paper" after acidity so that it will combine with sodium or which the composite article is subjected to a curnitrogen alkahs and form Water ing i The'proportioni of ngnm i pounds which can be precipitated :by adding V d wlqely dependmg upon how .much hgnm acids. In sulfite'cooking the lignin'of the wood is desired in the final product. As little as from is rendered soluble by the action of the Wood with 6 to 9% lignin based on the rubber is sufiicient cooking liquors' These extracts of lithe Wood to make the e e -@9 f bleither as such or partly purified are sometimes Q carbon blackhgnm copreclpltate mistakenly termed lign in "but are actually tammg 100 GRfiS 9 hgmn a d 45 lignin sulfonates. It is possible to treat l-ignin 'i black was prepared m the following sulfonates with alkali to convert them to a form V which is insoluble in water but soluble in alkaline A 9 of hgnm was first made prepar' solution the same as sulfate or oda li ni'n ing a slurry of 2.5 lbs. thereof in 74 lbs. of water When so treated such sulfite ligninzmuld g and then adding =1lb. of 50% caustic soda. In Within the nurviw of our inventiofl p this lignin solution was dispersed 22.5 lbs. of The Hgnih used in the foregoing k was Garbo? black h f t 100 of mixture obtained by first concentrating the black liquor cpntamed 25% hgmn m the form sodium from the sulfate cooking of pine wood, removing rligioatg an? fagbOl; black. I t f tall oil skimmings, lowering the pH of the liquor f th S i x fi g lg by treatment with carbon dioxide gas. and 0 f 10 O e coagulating the lignin by heat and urifying by gi k g fi hgmn and 225% carbon acid Washing he lignin so made is a dry powac An .18 0 su uric acid solution was pre- W J -1. pared by adding 0.34 lb. of 60 B (77.7%) sulder havmg h followmg range of analysls' furic acid to 145 lbs. of water. This solution was Per Gen heated to 194 F. and th lignin-latex mixture Moisture slowly added thereto while agitating thoroughly. Ash Less. than The mixture was then filtered and washed. i S lf After washing, the coprecipitate of this corn- Methoxyl position was removed from the filter and was Dioxane insoiubles "Less h 1 redispersed in the manner of the preceding exmpl mixed w h h usual p ding agents A still further source of lignin suitable for the and then dried at 70 C. for 24 hours, then milled, purpose of th present'applicatign is t saccharimolded and cured. 6O fication of the wood and other ligneous vegetable While our invention involving the redispersion tt g th Scholier process and its medifi; f he li nin containin coa ulat d-la ex ru b r cations, which produces an insoluble ligneo'u's has been illustrated using a latex of GR-S, it will residue which is highly acidic, ontaining e be pp t that latices of other rubbers, 'i. e., sugars, hemicelluloses and other degradation natural or other artificial rubbers uc as the products of cellulose. This material is susceptible c p y of b ene and acrylonitrile (GR-A), to purification to yield a material suitable for the polymer of chlorobutadiene (GR M) etc. are copregj'pitafion t rubber equally applicable. We claim;

The redispersed mixture of rubber particles, 7 1 In th manufacture f haped and cured lisnin, additional f r in n s if pr s nt rubber articles the steps of preparing a mixture and ur-ins nd mp un ine a ents may, if deof a latex of a rubbery butadiene 1,3 polymer sired, be spray'dried and thedried material filled d a reinforcing .aggnt inciuding lign'in, i into mold-S and Cured- The p y d y g will precipitating said m xture and obtaining a copr'e preferably be conducted on the mixture which cipitate of said polymer and reinforcing agent has e -re r d uffi iently fluid bya'gitatio in whichsa'id polymer is in the form of wet substantially non-coalescent particles, separating same from the attendant solution to yield a wet mass which is substantially free from acid and water soluble material and in which said polymer particles are still substantially non-coalescent, dispersing rubber compounding agents in said mass to yield an aqueous dispersion containing the polymer, reinforcing agent and rubber compounding agents, and drying the dispersion so formed.

2. The method of compounding a rubbery butadiene 1,3 polymer which comprises mixing a latex containing said polymer with an alkaline solution of lignin, acid precipitating the mixture and obtaining a polymer lignin coprecipitate in the form of wet non-coalescent particles, separating the same from the attendant solution-to yield a wet mass substantially free from acid and water soluble material and in which the polymer particles are still substantially non-coalescent, dispersing rubber compounding agents therein to yield an aqueous dispersion containing the polymer, lignin, and rubber compounding agents and drying the dispersion so formed.

3. The method of compounding a rubbery butadiene 1,3 polymer which comprises mixing a latex containing said polymer with an alkaline solution of lignin, acid precipitating the mixture and obtaining a polymer lignin coprecipitate in the form of wet non-coalescent particles, separating the same from the attendant solution to yield a wet mass substantially free from acid and water soluble material and in which the polymer particles are still substantially non-coalescent, dispersing rubber compounding agents therein to yield an aqueous dispersion containing the polymer, lignin, and rubber compounding agents and spray drying the dispersion so formed to yield a divided material ready for forming and curing.

4. The method of compounding a rubbery butadiene 1,3 polymer which comprises mixing a latex containing said polymer with an alkaline solution of lignin and incorporating in the mixture a reinforcing agent; acid precipitating the mixture and obtaining a coprecipitate in the form of wet substantially non-coalescent particles containing the polymer, lignin and reinforcing agent; separating the aqueous dispersion from the attendant solution to yield a wet mass substantially free from acid and water soluble material and in which the polymer particles are still substantially non-coalescent; dispersing rubber compounding agents therein and drying the dispersion so formed.

5. The method according to claim 4 in which the reinforcing agent is carbon black.

6. The method according to claim 1 in which the latex is that of butadiene-styrene copolymer.

'7. The method according to claim 2 in which the latex is that of butadiene-styrene copolymer.

8. The method according to claim 3 in which the latex is that of butadiene-styrene copolymer.

9. The method according to claim 1 including the step of milling the dried product containing uncured dispersed rubber particles for a time necessary to form a sheet.

10. The method according to claim 2 including the step of milling the dried product containing uncured dispersed rubber particles for a time necessary to form a sheet.

11. The method according to claim 1 in which the lignin present is at least 6% based on the rubber.

12. The method according to claim 4 in which the latex isthat of butadiene styrene copolymer.

13. The method according to claim 1 in which the latex is that of natural rubber.

14. The method according to claim 2 in which the latex is that or" natural rubber.

15. The method according to claim 3 in which the latex is that of natural rubber.

16. The method according to claim 4 in which the latex is that of natural rubber.

17. The method according to claim 1 in which the latex is that of the copolymer of butadiene and acrylonitrile.

18. The method according to claim 2 in which the latex is that of the copolymer of butadiene and acrylonitrile.

19. The method according to claim 3 in which the latex is that of the copolymer of butadiene and acrylonitrile.

20. The method according to claim 4 in which the latex is that of the copolymer of butadiene and acrylonitrile.

21. The method according to claim 1 in which the latex is that of the polymer of chlorobutadiene.

22. The method according to claim 2 in which the latex is that of the polymer of chlorobutadiene.

23. The method according to claim 3 in which the latex is that of the polymer of chlorobutadiene.

24. The method according to claim 4 in which the latex is that of the polymer of chlorobuta diene.

25. A product made by the process of claim 3.

26. A product made by the process of claim 3 in which the polymer is butadiene-styrene.

27. A product made by the process of claim 3 in which the polymer is butadiene-acrylonitrile.

28. A product made by the process of claim 3 in which the polymer is chlorobutadiene.

ARTHUR POLLAK. JOHN J. KEILEN, JR.

REFERENCES CITED The following references are of record in the file of this patent: 1

UNITED STATES PATENTS dustrial Chemical Sales Division of West Virginia Pulp and Paper Co., copyrighted on August 30, 1946 (30 pages). 

1. IN THE MANUFACTURE OF SHAPED AND CURED RUBBER ARTICLE THE STEPS OF PREPARING A MIXTURE OF A LATEX OF A RUBBERY BUTADIENE 1,3 POLYMER AND A REINFORCING AGENT INCLUDING LIGNIN, ACID PRECIPITATING SAID MIXTURE AND OBTAINING A COPRECIPITATE OF SAID POLYMER AND REINFORCING AGENT IN WHICH SAID POLYMER IS IN THE FORM OF WET SUBSTANTIALLY NON-COALESCENT PARTICLES, SEPARATING SAME FROM THE ATTENDANT SOLUTION TO YIELD A WET MASS WHICH IS SUBSTANTIALLY FREE FROM ACID AND WATER SOLUBLE MATERIAL AND IN WHICH SAID POLYMER PARTICLES ARE STILL SUBSTANTIALLY NON-COALESCENT, DISPERSING RUBBER COMPOUNDING AGENTS IN SAID MASS TO YIELD AN AQUEOUS DISPERSION CONTAINING THE POLYMER, REINFORCING AGENT AND RUBBER COMPRISING AGENTS, AND DRYING THE DISPERSION SO FORMED. 